In short, from what I have found on my previous search for the answer to this question is once it is detached and reattached you lose the self-tracking ability which means you have to spin through the property and check the original db value.
I found this article after a brief search.
http://msdn.microsoft.com/en-us/data/jj613924.aspx
I found this article after a brief search.
http://msdn.microsoft.com/en-us/data/jj613924.aspx